PingMonitor

PingMonitor polls your WoW latency and keeps track of your highest, lowest and average ping.
It is designed to be extremely lightweight and unobtrusive.
PingMonitor was built specifically to aid users of the TruePing.net service in gauging improvements in latency - however it is available and useful for anyone.

In short, it will monitor your ping :-P

When used in conjunction with TruePing software, this addon will enable the submission of latency statistics to TruePing.net.

How to read the display
"B" indicates your best ping - the lowest your latency has been (never zero).

"C" indicates your current ping - this is the same as the latency reported by the WoW client. In brackets after this figure is your average latency so far.